1. Field of the Invention
The present invention relates generally to the field of low voltage, high current DC rectifier circuits. More particularly, the present invention relates to utilization of both symmetrical and asymmetrical, normally off Junction Field Effect Transistors (JFET) to construct full wave rectifier circuits useful in low voltage and high current density DC applications.
2. Related Art
The increasing trend toward lower supply voltages for active semiconductor devices and Integrated Circuits (IC""s) has accelerated the search for more efficient low voltage power sources. Conventional power supplies utilizing full wave rectifier circuits constructed with silicon diode rectifiers are unacceptable in low voltage applications due to the excessive voltage drop across the forward biased diode terminals. Power loss in the diodes becomes excessive when they are used as rectifiers in a DC power supply designed for a terminal voltage as low as 3.0 volts.
Semiconductor diodes are combined with active devices to form circuits capable of producing low value DC supply voltages, but such circuits are generally not capable of handling the large currents frequently required. They usually exhibit a fairly large internal resistance and as such are very inefficient power sources. Furthermore, the number and complexity of steps required in the processing of this type of circuit as an IC also increases with the number of devices included.
Active semiconductor devices are used as switches in circuit arrangements producing DC power supply voltages, as for example in switched mode power supplies. Junction Field Effect Transistors (JFET) are frequently used as switches because they are easily switched between an ON or conducting state and an OFF or non-conducting state. Most importantly, the current carriers in a JFET are all majority carriers which results in short switching times. However, when operated at lower voltages, JFETs exhibit an internal resistance in the ON state that make them unsatisfactory and inefficient in applications requiring large currents.
Utilizing two copending applications, Ser. No. 09/430,500 and Ser. No. 60/167,959 and 09/708,336, all by Ho-Yuan Yu, and incorporated herein by reference, embodiments of the efficient full wave rectifiers of the present invention can be made.
Accordingly, what is needed is a semiconductor circuit that can efficiently supply the DC currents required in both discrete and integrated circuits being operated at low DC supply voltages. What is further needed is a full wave, low voltage, power rectifier circuit manufactured as an integrated circuit that is a pin for pin replacement for the full wave rectifiers used in conventional DC power supply circuits. What is also needed is a full wave rectifier circuit that has a very low internal resistance such that the power dissipated in the rectifier circuit itself is only a fraction of that delivered to a connected load. What is needed yet is a full wave rectifier circuit that exhibits short switching times between an on or conducting state and an off or non-conducting state. The present invention provides these advantages and others not specifically mentioned above but described in the sections to follow.
A full wave rectifier circuit that can efficiently supply the DC currents required in both discrete and integrated circuits being operated at low DC supply voltages is disclosed. In the present invention, four symmetrical, enhancement mode, Junction Field Effect Transistors (JFET) are connected to form a full wave rectifier circuit having two input terminals and two output terminals. In one embodiment, each JFET may have a starter device connected between source and drain, and a current limiting circuit in series with the gate lead. With an external voltage applied between the gate and either the source or the drain with a polarity that will forward bias the p-n junctions, low resistance, current conducting channels are formed between source and drain. This is the on or current conducting state for each JFET. Due to the biasing of the gate voltage, the voltage drop between source and drain of the normally off JFET in the on state is less than 0.1 volt, depending on device design.
With an external voltage applied between the gate and either the source or the drain with a polarity that will reverse bias the p-n junctions, the built-in p-n junction depletion regions will isolate the source and drain leads to prevent the conduction of electric current between source and drain. This is the off or non conducting state or each JFET. Thus, each JFET has a forward or current conducting state and a reverse or non current conducting state similar to a conventional semiconductor diode. Two n-channel and two p-channel JFETs are used to replace of the four semiconductor diodes found in a conventional full wave rectifier circuit. The gate leads of the JFETs are connected to the input terminals of the circuit such that a full wave rectified version of the input signal is produced at the output of the circuit.
In a second embodiment, four asymmetrical, enhancement mode, Junction Field Effect Transistors (JFET) are connected to form a full wave rectifier circuit having two input terminals and two output terminals. The gate of each JFET is electrically connected to its source. With an external voltage applied between source and drain with a polarity that will forward bias the p-n junctions between gate and drain, low resistance, current conducting channels are formed between source and drain. This is the on or current conducting state. The forward voltage drop of this embodiment is approximately the threshold voltage of the normally off JFET.
With an external voltage applied between source and drain with a polarity that will reverse bias the p-n junctions between gate and drain, the built-in p-n junction depletion regions will isolate the source and drain leads to prevent the conduction of electric current between source and drain. This is the off or non conducting state. Thus, each JFET has a forward or current conducting state and a reverse or non current conducting state similar to a conventional semiconductor diode. Two n-channel and two p-channel JFETs are used to replace of the four semiconductor diodes found in a conventional full wave rectifier circuit. A full wave rectified version of the input signal is produced at the output of this circuit.